improve java.sql.Wrapper support

src/main/java/com/alibaba/druid/proxy/jdbc/PreparedStatementProxyImpl.java

@@ -473,13 +473,4 @@ public class PreparedStatementProxyImpl extends StatementProxyImpl implements Pr
     public String getLastExecuteSql() {
         return this.sql;
     }
-
-    @SuppressWarnings("unchecked")
-    public <T> T unwrap(Class<T> iface) throws SQLException {
-        if (iface == PreparedStatement.class) {
-            return (T) statement;
-        }
-
-        return super.unwrap(iface);
-    }
 }